test: dm: add ofnode_graph tests

Test suit for of_graph parsing helpers.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index b8f3012..8029195 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -2048,6 +2048,61 @@
 			sandbox,err-step-size = <512>;
 		};
 	};
+
+	graph1 {
+		ports {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			port@0 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				reg = <0>;
+
+				endpoint@0 {
+					reg = <0>;
+				};
+
+				endpoint@1 {
+					reg = <1>;
+				};
+			};
+
+			port@1 {
+				reg = <1>;
+
+				endpoint {
+					test-property-0;
+				};
+			};
+
+			port@2 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				reg = <2>;
+
+				graph2_link: endpoint@0 {
+					reg = <0>;
+					test-property-1;
+					remote-endpoint = <&graph1_link>;
+				};
+
+				endpoint@1 {
+					reg = <1>;
+				};
+			};
+		};
+	};
+
+	graph2 {
+		port {
+			graph1_link: endpoint {
+				remote-endpoint = <&graph2_link>;
+			};
+		};
+	};
 };
 
 #include "sandbox_pmic.dtsi"